In our co-pending French Patent Application No. 87 17072 (U.S. patent application Ser. No. 281,028 filed Dec. 7, 1988, now U.S. Pat. No. 4,969,855; United Kingdom Patent Application No. 88 28253.8) we have described a damper of the above kind, having additional circumferentially acting resilient means. These are of relatively low stiffness, separate from each other, with one being arranged between the hub and one of the hub plates, and the other being arranged between the hub and the other hub plate. These resilient means are mounted in slots or recesses formed in the outer periphery of the hub and in the inner periphery of the hub plates. An alternative arrangement of the loose coupling means is provided, such that, for a first circumferential direction of the relative angular displacement between the first and the second of the the parts of the assembly, only one of the hub plates operates initially, while in the opposite circumferential direction, while it is still true that only one of the hub plates operates, in this case it is the other one.
When the clearances in the loose coupling means are different, it is possible to obtain a summation of the effects of the two additional resilient means, resulting in a beneficial accumulated stiffness favourable to reduction in noise, which is caused especially when the clearance in the loose coupling means is taken up. During this phase, the hub plates are made to rotate together, by virtue of the resilient means of greater stiffness that acts between the second and third of the three parts of the assembly.
Such an arrangement does not however enable the stiffness of the additional resilient means to be readily overcome, since, in arranging the resilient means to carry out their principal function, one of the resilient means is such as to act mainly in one circumferential direction while the other is such as to act in the opposite circumferential direction.